Intermolecular Forces

Analysis:

2. Of the alcohols tested 1-Butanol was found to contain the strongest intermolecular forces (IMF) of attraction, with Methanol containing the weakest. It was discovered through experimentation that Methanol induced the highest ?T of all alcohols tested, and that conversely 1-Butanol induced the lowest ?T. The atomic structure of all four alcohols is very similar, as starting with 1-Butanol a CH2 group is lost as you move from 1-Butanol to 1-Propanol to Ethanol and then again to Methanol. Each structure is fairly linear and contains an H-bond with Oxygen, so the real change is found in the loss of the CH2 group, this lowers the liquid’s Molecular Mass, thus lowering the London forces as you move from 1-Butanol through 1-Propanol and Ethanol, to Methanol. Since the IMF within 1-Butanol are stronger than the other three alcohols, it has a higher ?Hvap. During the experiment, all 4 alcohols tested (indeed all 7 liquids tested) were exposed to the room temperature air of the laboratory. Thus the free-floating gas particles in the lab air were able to impart Kinetic Energy to the liquids being sampled, at a constant rate under fairly controlled and consistent conditions. This resulted in the kinetic energy being absorbed into the liquid from the air surrounding the temperature probe, causing said air to drop in temperature, which was duly reported by the probe, and used to calculate the ?T of the liquid. In the case of 1-Butanol the ?T was very small, indeed smaller than any other liquid tested. It also took a very long time comparatively to reach its minimum, as opposed to a liquid with a high ?T like Methanol which was quite fast. An inverse relationship is found then between the ?T and the strength of the IMF ...

... middle of paper ...

... each liquid. With molecular weight, as the weight increased the strength of the IMF, namely London forces increased as well. Then as the IMF increased the propensity of the liquid to evaporate was lessened, leading both to a lower ?T and a slower time to reach the ?T in general.

Conclusion:

In conclusion it was found that there is an inverse relationship between the strength of the intermolecular forces holding molecules together and the rate at which those molecules evaporate. As the bonds get stronger it takes more energy to separate them and allow the molecules to escape into the vapor phase. This was the goal of the lab and it was met. Significant improvements could only be made at a considerable investment in time and expense and are unnecessary as the lab procedure as outlined was more than enough to derive the relationship needed through comparison.